Support Explicit Backed Enum casting

Description

The following code:

https://3v4l.org/pfXH4#v8.5.3

<?php

echo '----- Backed integer enum -----'.PHP_EOL;
enum DayOfWeekInt : int
{
    case Monday = 1;
    case Tuesday = 2;
    case Wednesday = 3;
    case Thursday = 4;
    case Friday = 5;
    case Saturday = 6;
    case Sunday = 7;
}
$var = DayOfWeekInt::Monday;

try {
    echo '--- intval($var) --'.PHP_EOL;
    echo intval($var);    
} catch (\Throwable $ex) {
    echo $ex;
}
echo PHP_EOL;

try {
    echo '--- (int) $var ---'.PHP_EOL;
    echo (int) $var;
} catch (\Throwable $ex) {
    echo $ex;
}
echo PHP_EOL;

echo PHP_EOL;
echo '----- Backed string enum -----'.PHP_EOL;
enum DayofWeekString : string
{
    case Monday = 'monday';
    case Tuesday = 'tuesday';
    case Wednesday = 'wednesday';
    case Thursday = 'thursday';
    case Friday = 'friday';
    case Saturday = 'saturday';
    case Sunday = 'sunday';
}
$var = DayofWeekString::Monday;

try {
    echo '--- strval($var) ---'.PHP_EOL;
    echo strval($var);
} catch (\Throwable $ex) {
    echo $ex;
}
echo PHP_EOL;
    
try {
    echo '--- (string) $var ---'.PHP_EOL;
    echo (string) $var;
} catch (\Throwable $ex) {
    echo $ex;
}
echo PHP_EOL;

Resulted in this output:

----- Backed integer enum -----
--- intval($var) --

Warning: Object of class DayOfWeekInt could not be converted to int in /in/pfXH4 on line 18
1
--- (int) $var ---

Warning: Object of class DayOfWeekInt could not be converted to int in /in/pfXH4 on line 26
1

----- Backed string enum -----
--- strval($var) ---
Error: Object of class DayofWeekString could not be converted to string in /in/pfXH4:48
Stack trace:
#0 {main}
--- (string) $var ---
Error: Object of class DayofWeekString could not be converted to string in /in/pfXH4:56
Stack trace:
#0 {main}

But I expected this output instead:

no warnings, no errors and a correct explicit conversion.

----- Backed integer enum -----
--- intval($var) --
1
--- (int) $var ---
1

----- Backed string enum -----
--- strval($var) ---
monday
--- (string) $var ---
monday

PHP Version

PHP 8.5.3

Operating System

No response

Start by running the provided PHP 8.5.3 reproduction from the issue and compare explicit integer and string casts for backed enums. Trace the enum casting behavior in the PHP source, then add coverage for the expected values and absence of warnings or errors. Done means all four conversions produce the backed values shown in the report.